While the possible involvement of beta2-microglobulin in cytotoxic T lymphocytes (CTL) recognition events is still under investigation, with no conclusive results emerging from this study yet, concrete progress made in several other areas includes: (1) the dml mutant is shown to express a hybrid H-2Dd/H-2Ldprotein that is probably the product of fused genes; (2) CTL responses to cell surface-coupled proteins can now be studied since we developed a way of covalently conjugating a million or more protein molecules to cells that then remain viable and stable for over a day in culture and that serve as excellent targets for lysis by antibody plus complement and ADCC; (3) we discovered that some monoclonal antibodies are excellent ADCC mediators and that ADCC efficiency depends both on the subclass (IgG2a or IgG3) and the orientation of the antibody on the cell; (4) normal human lymphocytes are not good ADCC targets; (5) human K effectors induce rapid fragmentation of the nuclear DNA in mouse target cells; and (6) nuclear DNA fragmentation is induced in mouse target cells only and not in human target cells when such targets are lysed by ADCC, CTL, or NK cells. (CS)